1. Field of the Invention
The present invention relates to a liquid jet recording process and apparatus therefor, and more particularly to such process and apparatus in which a liquid recording medium is made to fly in a state of droplets.
2. Description of the Prior Art
So-called non-impact recording methods have recently attracted public attention because the noise caused by at the recording can be reduced to a negligible order. Among these, particularly important is the so-called ink jet recording method allowing high-speed recording on a plain paper without particular fixing treatment, and in this field there have been proposed various approaches including those already commercialized and those still under development.
Such ink jet recording, in which droplets of a liquid recording medium, usually called ink, are made to fly and to be deposited on a recording member to achieve recording, can be classified into several processes according to the method of generating said droplets and also to the method of controlling the direction of flight of said droplets.
A first process is disclosed for example in the U.S. Pat. No. 3,060,429 (Teletype process) in which the liquid droplets are generated by electrostatic pull, and the droplets thus generated on demand are deposited onto a recording member with or without an electric-field control on the flight direction.
More specifically said electric-field control is achieved by applying an electric field between the liquid contained in a nozzle having an orifice and an accelerating electrode thereby causing said liquid to be emitted from said orifice and to fly between x-y deflecting electrodes so arranged as to be capable of controlling the electric field according to the recording signals, and thus selectively controlling the direction of flight of droplets according to the change in the strength of the electric field to obtain deposition in desired positions.
A second process is disclosed for example in the U.S. Pat. No. 3,596,275 (Sweet process) and in the U.S. Pat. No. 3,298,030 (Lewis and Brown process) in which a flow of liquid droplets of controlled electrostatic charges is generated by continuous vibration and is made to fly between deflecting electrodes forming a uniform electric field therebetween to obtain a recording on a recording member.
More specifically, in this process, a charging electrode receiving recording signals is provided in front of and at a certain distance from the orifice of a nozzle constituting a part of a recording head equipped with a piezo vibrating element, and a pressurized liquid is supplied into said nozzle while an electric signal of a determined frequency is applied to said piezo vibrating element to cause mechanical vibration thereof, thereby causing the orifice to emit a flow of liquid droplets. As the emitted liquid is charged by electrostatic induction by the above-mentioned charging electrode, each droplet is provided with a charge corresponding to the recording signal. The droplets having thus controlled charges are subjected to deflection corresponding to the amount of said charges during the flight in a uniform electric field between the deflecting electrodes in such a manner that only those carrying recording signals are deposited onto the recording member.
A third process is disclosed for example in the U.S. Pat. No. 3,416,153 (Hertz process) in which an electric field is applied between a nozzle and an annular charging electrode to generate a mist of liquid droplets by continuous vibration. In this process the strength of the electric field applied between the nozzle and the charging electrode is modulated according to the recording signals to control the dispersion of liquid thereby obtaining a gradation in the recorded image.
A fourth process, disclosed for example in the U.S. Pat. No. 3,747,120 (Stemme process), is based on a principle fundamentally different from that used in the foregoing three processes.
In contrast to said three processes in which the recording is achieved by electrically controlling the liquid droplets emitted from the nozzle during the flight thereof and thus selectively depositing only those carrying the recording signals onto the recording member, the Stemme process is featured in generating and flying the droplets only when they are required for recording.
More specifically, in this process, electric recording signals are applied to a piezo vibrating element provided in a recording head having a liquid-emitting orifice to convert said recording signals into mechanical vibration of said piezo element according to which the liquid droplets are emitted from said orifice and deposited onto a recording member.
The foregoing four processes, though being provided with respective advantages, are however associated with drawbacks which are inevitable or have to be prevented.
The foregoing first to third process rely on electric energy for generating droplets or droplet flow of liquid recording medium, and also on an electric field for controlling the deflection of said droplets. For this reason the first process, though structurally simple, requires a high voltage for droplet generation and is not suitable for high-speed recording as a multi-orificed recording head is difficult to make.
The second process, though being suitable for high speed recording as the use of multi orificed structure in the recording head is feasible, inevitably results in a structural complexity and is further associated with other drawbacks such as requiring a precise and difficult electric control for governing the flight direction of droplets and tending to result in formation of satellite dots on the recording element.
The third process, though advantageous in achieving recording of an improved gradation by dispersing the emitted droplets, is associated with drawbacks of difficulty in controlling the state of dispersion, presence of background fog in the recorded image and being unsuitable for high-speed recording because of difficulty in preparing a multi-orificed recording head.
In comparison with the foregoing three processes the fourth process is provided with relatively important advantages such as a simpler structure, absence of a liquid recovery system as the droplets are emitted on demand from the orifice of a nozzle in contrast to the foregoing three processes wherein the droplets which do not contribute to the recording have to be recovered, and a larger freedom in selecting the materials constituting the liquid recording medium not requiring electro-conductivity in contrast to the first and second processes wherein said medium has to be conductive. On the other hand said fourth process is again associated with drawbacks such as difficulty in obtaining a small head or a multi-orificed head because the mechanical working of a head is difficult and also because a small piezo vibrating element of a desired frequency is extremely difficult to obtain, and inadequacy for high-speed recording because the emission and flight of liquid droplets have to be performed by the mechanical vibrating energy of the piezo element.
As explained in the foregoing, the conventional processes respectively have advantages and drawbacks in connection with the structure, applicability for high-speed recording, preparation of recording head, particularly of a multi-orificed head, formation of satellite dots and formation of background fog, and their use has therefore been limited to the fields in which such advantages can be exploited.